The National Park Service and the nonprofit Yosemite Fund are undertaking a project to rebuild close to 100 miles of trails in Yosemite National Park that range from the popular loop trail around Yosemite Valley to miles of spectacular hiking paths in the High Sierra.

The project will cost about $13 million -- with about $3 million from government funds and $10 million from private donations.

"Some of these trails have been neglected for a long time," said Park Superintendent Michael Tollefson, who said better trails "will help get people out of cars. It will be a great boon for a much better trail system."

The project to be formally launched at a San Francisco news conference today will include high-profile trails like the northern end of the famous John Muir Trail, which extends from the Happy Isles in Yosemite Valley and eventually runs more than 200 miles to the summit of Mt. Whitney in Sequoia National Park.

Another improvement would rebuild 33 miles of the Muir Trail in Yosemite from the valley up to Tuolumne Meadows and then along the Lyell Fork of the Tuolumne River and over Donahue Pass into the Ansel Adams wilderness.

Also included is restoration of foot trails in the Mariposa Grove of big trees where about 7.5 miles of trails lead from a parking area into a famous grove of giant Sequoias.

Other projects involve trails over Red Peak Pass, improvements on trailheads on the Tioga Road and repairs to a trail leading to the summit of 10,850-foot Mt. Hoffmann in the center of the park.

Some of the trails are in worse shape than others.

The portal to the Muir Trail at the Happy Isles also leads to Vernal and Nevada Falls -- "the gateway to the wilderness," Tollefson calls it. Most visitors only get as far as the bridge below Vernal Fall, but some head into Little Yosemite Valley, and still others head off into the high country. "It's the portal to the southern Sierra," Tollefson said.

Now the beginning of the trail "looks like somebody ran over it with a bulldozer," he said. That's the result of a flood eight years ago, heavy use, erosion and minimal maintenance.

Only about 6 percent of Yosemite Park is reached by roads; the rest, including the crest of the Sierra, is covered by 800 miles of trails. Many of them, Tollefson said, are "significantly eroded."

"We are behind the curve in taking care of them," he said.

The main reason is that scarce federal resources generally go to buildings and roads. Money for other projects has to come from private donations, through nonprofit groups like the Yosemite Fund, one of the organizations the park service calls "park partners."

Last year, the fund helped bankroll a $13.5 million restoration of the approach to Yosemite Falls. Over the last 18 years the Yosemite Fund has raised more than $35 million for Yosemite projects.

The fund announced a $1 million gift from David and Dana Dornsife of Danville for the latest project. Dornsife is a businessman with interests in steel and bus construction.